While it may not be the largest World Heritage Area on Earth, the Great Barrier Reef is one of the better known.

Its biological diversity is also unmatched by any other World Heritage Area.

Covering 348,000 square kilometres, this vast expanse is bigger than the United Kingdom, Holland and Switzerland combined.

The World Heritage Area extends from the top of Cape York in north-east Australia to just north of Bundaberg, and from the low water mark on the Queensland coast to the outer boundary of the Marine Park, which is beyond the edge of the continental shelf.

About 99 per cent of the World Heritage Area is within the Great Barrier Reef Marine Park.

The remaining one per cent includes:

some 980 islands which are under Queensland jurisdiction

some internal waters or Queensland (for examples, some deep bays, narrow inlets or channels between islands)

intertidal areas protected by Queensland legislation

a number of small exclusion areas (state waters) around major ports and urban centres.

Within the World Heritage Area, there are more than 3000 separate coral reefs.

There are also 1050 islands and cays - these include 600 continental islands and 300 coral cays, while the remaining 150 islands are inshore mangrove islands which are important to the functioning and health of the Great Barrier Reef.

Together, the biodiversity and interconnectedness between species and habitats represents one of the richest and most complex natural ecosystems on earth.

The Great Barrier Reef was declared a World Heritage Area in 1981 because of its 'outstanding universal value'. This recognised the Reef as being one of the most remarkable places on earth, as well as its global importance and its natural worth.

The World Heritage Committee listed the Reef for all four natural criteria:¹

Be outstanding examples representing the major stages of the earth's evolutionary history